The present invention relates to cameras, and more particularly to a new form of display system therefor.
While not intending to be limited thereby, the background of the present invention and the concepts of the present invention will be described in the environment of a single lens reflex (SLR) camera. Such cameras typically include an objective lens, or interchangable objective lenses, and a camera body to which the lens is attached. The camera body houses the film, shutter, associated viewing optics and display, and a light sensor and electronic control circuit for controlling either the speed of the shutter or the opening of the aperture diaphragm or both. The diaphragm (iris) usually is contained within the objective lens assembly.
Cameras of this nature have included various forms of displays. Typical examples include a meter with a pointer used in the "match needle" type systems, illuminated indicia to indicate taking parameters, and the like. The above-referenced application discloses, inter alia, a new form of electronic system for cameras and new forms of display systems therefor.
The present invention provides a simplified form of display system for a camera. The usual objective lens has a given f-stop range of eight to nine f-stops, and the open aperture value (A.sub.o, such as f 1.4, f 2, etc.) varies from lens to lens. The light sensing system measures light passing through the objective lens being used and the resulting electrical signal is a function of brightness (B) and the open aperture value (A.sub.o) of the lens in use. Instead of entering a separate electrical signal for A.sub.o, the calculations of aperture value are performed with a "relative" aperture value since ratios are involved in the calculations. However, an absolute aperture value is needed for display to the camera user, and this value is derived by performing a combined electrical and mechanical summation. More particularly, an electrical signal representing a relative aperture value (such as A.sub.c -A.sub.o) and a fixed aperture parameter (such as A.sub.o) are mechanically added to thereby derive an absolute aperture value (eg., A.sub.c) for display to the camera user. This is accomplished in an exemplary embodiment by physically moving an aperture scale as a function of the fixed aperture value while electrically providing the relative aperture value through an electrical meter, series of light sources, or the like. This system enables simplification of the aperture potentiometer system, the camera electronics and display, and provides an automatic reduction of the f-stop range to be used in the calculations and display.
Accordingly, a principal object of the present invention is to provide an improved display system for photographic devices.
Another object of the present invention is to provide an improved form of camera system wherein electrical computations are performed using a relative aperture value signal, and an absolute aperture value is derived for display by performing a combined electrical and mechanical summation.